Description

A study of heat transfer and pressure drop characteristics for single-phase and twophase
flow of refrigerants in micro channel tubes was conducted. An existing facility was
modified to perform tests on a single microchannel tube using water flowing in counterflow
as the heat sink fluid. Data were collected for sub cooled liquid, superheated vapor and
condensing refrigerant for circular-port microchannel tubes at four different mass flow
rates. The refrigerants tested were R-22, R-134a and R-407C. In addition to circularport
tubes, square-port tubes were tested with R-22 for both single-phase and two-phase
flow. Data were also taken with water flowing inside a square-port microchannel tube.
The Reynolds number for all the flows in this study ranged from 3,000 to 17,000 in the
liquid phase and 30,000 to 110,000 in the vapor phase.
The heat transfer coefficients and pressure drop for circular-port micro channel tubes
were compared for R-22, R-134a and R-407C. For sub cooled liquid flow, the heat transfer
coefficient for R-407C was found to be greater than that for R-22 and R-134a. The heat
transfer coefficient for R-22 was found to slightly lesser than the other two refrigerants
for condensing flow.
A model was built to predict the heat transfer and pressure drop in the microchannel
tube. In most cases, the heat transfer and pressure drop predicted by the model agree
very well with experimental results. A sensitivity analysis revealed that the total heat
transfer is not very sensitive to the refrigerant side heat transfer coefficient.

Issue Date:

1997-11

Publisher:

Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.